When the Arctic warmed after the ice age 10,000 years ago, it created perfect conditions for drought. According to new research led by Bryan Shuman, a professor in the Department of Geology and Geophysics at the University of Wyoming, similar changes could be in store today because a warming Arctic weakens the temperature difference between the tropics and the poles. This, in turn, results in less precipitation and weaker mid-latitude westerly wind flow leading to prolonged drought. When the temperature difference between the tropics and the poles are wider, the result is more precipitation, intense cyclones and more robust wind flow. However, due to the Arctic ice melting and warming up the poles, those disparate temperatures are becoming closer.
In this study, the author takes a global approach and relates the history of severe dry periods of temperature changes. Importantly, when temperatures have changed in similar ways to today (warming of the Arctic), the mid-latitudes, particularly places like Wyoming and other parts of central North America have dried out. Climate models anticipate similar changes in the future.
Currently, the northern high latitudes are warming at rates that are double the global average. This will decrease the equator-to-pole temperature gradient to values comparable with the early to middle Holocene Period. According to the paper, geological evidence helped to estimate how dry conditions have been in the past 10,000 years. Lakes are these natural recorders of wet and dry conditions and when lakes rise or lower, they leave geological evidence behind. The researchers' Holocene temperature analysis included 236 records from 219 sites. During the past 10,000 years, many of the lakes studied were lower earlier in history than today.
The research group looked at the evolution of the tropic-to-pole temperature difference from three time periods: 100 years ago, 2,000 years ago and 10,000 years ago. For the last 100 years, many atmospheric records facilitated the analysis but, for the past 2,000 years or 10,000 years, there were fewer records available. Tree rings can help to expand studies to measure temperatures over the past 2,000 years, but lake deposits, cave deposits and glacier ice were studied to record prior temperatures and precipitation. According to the study, geological evidence provides an excellent test to validate computer models that make forecast for some other time period.
Cody C. Routson, Nicholas P. McKay, Darrell S. Kaufman, Michael P. Erb, Hugues Goosse, Bryan N. Shuman, Jessica R. Rodysill, Toby Ault. Mid-latitude net precipitation decreased with Arctic warming during the Holocene. Nature, 2019; DOI:10.1038/s41586-019-1060-3
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© 2019 Oceanographer Daneeja Mawren